fracture surface

[aldone]

hi all,
I have one question for your attention on test material...
I know that for the torsion test i have:
1)Shear (ductile) failure is along the maximum shear plane (90 degreed)
2) Tensile (brittle) failure is perpendicular to the maximum
tensile stress (at 45o), resulting in a helical fracture
The question is:
only in torsion test i have this difference behavior for the surface failure between brittle and ductile material while for tensile and bendig testing i have always the surface failre perpedicular to maximum stress?
Tanks and best regards

 

[Compositepro]

Because you do not usually get high enough shear loads in those tests to get shear failures.

 

[metman]

A cylindrically shaped ductile tensile specimen will fail in a typical cup-cone configuration along shear planes rather than transverse (perpendicular).

Maybe someone will provide a link showing a photograph of a cup-cone failure. One picture is worth a lot of words.

 

[metman]

Here is a link:

http://www.sv.vt.edu/classes/MSE2094_NoteBook/97ClassProj/exper/bailey/

http://www/bailey.html

Scroll down to Fig. 8.1 and 8.3

Quote from my above post:
...ductile tensile specimen will fail in a typical cup-cone configuration along shear planes rather...

I should have said,"...primarily along shear planes..."

In the above post, I was visualizing a failure between Fig. 8.1a and 8.1b where the cup is much deeper and there is very little transverse fracture face, maybe even rounded. However, Fig. 8.1a certainly belies a perpendicular fracture face. The author states this condition (8.1a) as highly ductile but maybe he meant ideally ductile (not to be expected in reality). And yet I suppose I can picture a piece of cylindrical shaped pure Lead rupturing to a point?